How big is your room in proportion? And unless you've just moved in, it's probably not full of empty spaces with nothing there - maybe one or two 'tiles' of empty space, but not tons. Desks are about 2 tiles wide and 1 tile deep - single beds 3 tiles long, 1 tile wide, and double beds the same length and 2 tiles wide. A tile roughly equates to 3 feet or 1 meter. Look at the room you're sitting in, and try to figure out how many sim-tiles the room would be. While there are plenty of gigantic mansions out there in the real world, doing these well in-game is not a beginner project. Without any concept of sim-scale, most people build massive rooms that are way out of proportion with reality. This is one of the first stumbling blocks beginning builders run across.
Even if you're no architect or professional interior decorator, you can still make nice homes that look realistic and attractive, using these tips. Once you have the basic shell of your exterior done, you'll need to find some way to split up the cavernous interior space you've created, and furnish and decorate it.
